Reference will be made herein below to the repair of damaged cartilage. It should be understood that the damaged tissue may be other types of tissue including damaged surface bone itself. Reference will also be made herein below to the repair of cartilage of knee joints and again it should be understood that the present invention may be applied to other body joints and indeed to other organs of the body which consist of or incorporate bone.
Defects in the articular surfaces of the knee joint, especially in young active individuals, are currently a focus of interest by orthopaedic surgeons. It is desirable to repair such defects in order to prevent the articular damage from spreading, thereby leading to serious degenerative changes in the joint. Such changes may result in the need for a total knee replacement which is particularly undesirable in young active individuals with a long life expectancy. If the lifetime of the implant is less than that of the patient, a revision procedure may be necessary. Preferably, such revision procedures are to be avoided, having regard to inconvenience to the patient. Furthermore implant revision procedures are both lengthy and very costly. Various techniques for cartilage repair are either in current use or under development but publicly disclosed. The Osteochondral Autogenous Transplant System (OATS) of Arthrex Inc is perhaps the most widely used method. Osteochondral plugs are harvested from a healthy donor and, more particularly, from a site which is claimed to be ‘non-weight-bearing’. These plugs are transplanted into the site of the cartilage defect. This procedure has been applied primarily in the knee joint.
However, there are no donor sites in the knee with cartilage of a comparable thickness to that of the deficient site that can be described as ‘non-weight-bearing’ areas. The solcus terminalis, the most currently used site for harvesting such grafts, is in direct contact with the lateral meniscus at the position of full knee extension, and is therefore a weight-bearing site.
Furthermore, harvesting a large osteochondral plug from the solcus terminalis may cause the lateral meniscus to become lax and impair its load-bearing function. As a result, all the tibio-femoral loads would be transmitted onto the small area of direct contact between the femur and tibia. The resultant stresses could be as high as those arising after meniscectomy with its consequential degenerative changes in the cartilage of the tibial plateau. Such changes have always been regarded as precursors to osteo-arthritis.
While the OATS method provides a reasonable technique, including good instrumentation, for transplanting live autogenous grafts for repair of defects in cartilage, it involves introducing potentially damaging effects at other sites with the serious disadvantages discussed above. In addition, harvesting a plug from a donor site creates a new damage in the knee articular surface. For this reason, OATS would not be suitable for the repair of large defects. The use of OATS for small repairs would probably limit the magnitude of the problem discussed above, but it would also limit the indication for using this technique.
The technique known as Autogenous Chondrocyte Implants (ACI) of Genzyrne Inc is a conceptually elegant approach which is gaining popularity. The procedure is intended for repair of small as well as large irregular defects, and is achieved in two stages. In the first stage, chondrocytes (cartilage cells) are harvested from the patient and cultured in suspension. In the second stage of the operative procedure, cartilage residue is cleared from the repair site. The site is then covered with a piece of periosteal tissue which is sutured or glued to the perimeter of the repair area. The chondrocytes are then injected into the repair site using a hypodermic syringe, puncturing the periosteum with the needle of the syringe. In a variation of this procedure, the periosteal tissue is applied to the repair site in the first stage of the operation to ensure that, by the time the chondrocytes are due to be injected, an adequate seal has formed between the tissue and the perimeter of the cartilage. There is a high probability of the chondrocytes escaping through the hole of the hypodermic needle in either version of the procedure.
A further problem with the second version of the procedure is the probability of tissue adhesions occurring between the periosteal tissue and the bottom of the repair site.
This procedure has a low rate of success and the quality of cartilage in the repair site is questionable. As with the OATS method, this procedure is not minimally invasive. It is also a disadvantage that it requires two operative procedures although the first stage is less invasive as it can be performed arthroscopically.
A procedure proposed by Smith & Nephew involves the production of cartilage discs formed by allogeneic chondrocyte culture on an absorbable textile fabric. The discs are grown in the laboratory, the chondrocytes being cultured on a matrix of a non-woven mesh of a bioabsorbable material, typically polyglycolic acid. When this procedure is completed, the disc is supplied for implantation at the repair site.
An advantage of this method is that no damage to an intact healthy chondral site will occur since the method uses allogeneic sources. Furthermore the procedure is completed in a one stage operation.
The discs can be made in different sizes but there must be a limit to the size of the defect which can be repaired with a loose disc which is merely placed in the repair site. The implant could move freely in the joint. It could wrinkle under the influence of tangential forces and, as a result, could be completely damaged. This problem would be exacerbated by the low compressive modulus of the material.
A further disadvantage with this method is that the material, being an allograft, runs the risk of infection. Although a small risk, this is an inherent problem with any allograft.
A further problem to be anticipated with this type of graft is the compressive modulus of the material. It may be quite small and the material might be in need of conditioning to achieve a modulus compatible with that of cartilage of the surrounding area.
The DePuy cartilage repair system is a hexagonal disc of non-woven fabric made of a bioabsorbable material and which has a hard substrate that enables the implant to be attached to the bone. The hexagonal shape of the disc allows repair of damaged areas of irregular shapes by using a plurality of discs in a close-packed array. The disadvantages with this system are that the use of too many adjacent hexagonal discs will result in much damage to the bone substrate, and, further the technique may require considerable skill and its application may also be time consuming.